One goal of this project is to better understand the mechanisms of the Ionic conductances in membranes which are voltage dependent, i.e., excitable. Another goal is to determine how drugs influence these channels. Recent experiments using the squid giant axon have shown the drug, yohimbine, causes a reduction in sodium current which is reduced further when a depolarizing pulse train is applied. Studies have been made of the time course of the sodium current during the pulses and of the time course of the reduction in amplitude. The data can be fit by a model wherein yohimbine binds preferentially to open sodium channels and results in a slower rate of activation. Other studies are involved with the effects of oxygen pressure on the giant axon of Myxicola as well as the effects of calcium blockers on the barnacle muscle membrane. BIBLIOGRAPHIC REFERENCES: Henderson, J.V., Lowenhaupt, M.T., and Gilbert, D.L.: Helium pressure alteration of function in squid giant synapse. Undersea Biomed. Res. 4: 19-26, 1977. Howell, B.J. and Gilbert, D.L.: pH-Temperature dependence of the hemolymph of the squid, Loligo pealei. Comp. Biochem. Physiol. 55A: 287-289, 1976.